Head lamp



.April 26, 1927. 1,625,946

J. H. LAlRD HEADLAMP Filed Mrch 13. 1924 A TTOR/VEYJ.

Patented Apr. 26, 1927.

PATENT OFFICE.

JOHN H. LAIRD, OF LOUISVILLE, KENTUCKY.

HEAD LAME Application filed March 13, 1924. Serial No. 699,053.

My inventionrelates to headlamps for vehicles and the like, in which the object is to project the light without glare to approaching or passingpersons, `and still to illuminate with the highest efliciency those portions of the roadway which require it for safe driving.

It is my object in the first place to provide areflector based on other than a single parabola of revolution, and in defining the concavity of the refiector, it is my. object to provide for a definite series of curves, easy to plot for various sizes of lamps, and vhaving .definite action in the deflection of light` rays. Many of the refiectors of the patent. art require a combination of more than one refiector, and while a single cross section of such a combination inay be effective, it is exceedingly difiicult in manufacturing, making dies, etc., to provide for the plurality of meeting edges, and as a result the light rays are not refiected so as to give a maximum intensit-y from the source of light. i i

My reflector curves are designed to accomplish the following features: (a) A bright line of light in` a horizontal plane or dipping slightly from the height of the refiector which will'brilliantly light the road directly ahead of the Vehicles. (b) A diffused light illuminating the roadway at the sides without any rays which pass upwardly from the horizontal, so as to create a glare. (o) Bright light adjacent the vehicle and irninediately to the sides thereof for safety against accidentand so that when the headlanips are dimmed, there will be enough light to drive. It should be noted, however, that it is entirely unnecessary to dim the lights in my headlamps, except perhaps when the plane of the vehicle frame, as in passing over the brow of a| hill, is such as to project in improper angle to the road, although it will always maintain its angle to the vehicle.

I provide in addition for the use of a deflector element in the reflector which cuts out direct rays from the bulb, and defleots them back onto the main reflector in such a way as to waste no Candle power, but to avoid direct view of the bright spot in the lamp bulb from the front of the lamp.

I accomplish my objects by that certain construction and arrangement of parts to be hereinafter niore specifically pointed out and claimed'.

In the drawings:

Figure l is a diagrammatic section of a refiector taken on a Vertical plane through its center.

Figure 2 is a front elevation of the reflector also partially diagraminatic. v

Figure 3 is a perspective view of therefiector complete with deflecting element in place.

Figure -i is a section taken on a central vertical plane through Figure 3.

It is known that a catenary curve, possesses certain functions dependent upon the depth thereof as coinpared to the distance between its ends. A catenary is a curve which will be forined by a. fleXible element of uniforni character throughout, suspended from its ends. Such a curve has known functions which can be plotted by mathemat-ical formula, and can be used practically in forming dies, by means of which to form up a refiector.

A catenary curve is close to a parabola at its central portion or apex, and dependent upon the spacing of its ends with relation to its depth, i. e., its horizontal component, can be formed so as to tend toward an ellipse at its ends.

Thus I form the upper portion of my refiector by one half of a catenary curve 1, revolved on the aXis of the curve through a half circle. This portion of the refiector will then provide for general illumination of the roadway by light rays projecting at all angles cxcept upwardly from the horizontal.

In the diagram of Figure 1, the curve 1 is shown, and the nature of the curve is designed to provide the desired light pattern. By spreading the ends of the curve, the light rays can be given less and less convergence, until the ends pass beyond the liinits of a parabolic curve having coincidence at the apex and having a focal dist-ance equal to the parameter of the catenary. Thus the catenary of my refiector must have a horizontal component which is less than the component of a parabola having a focal distance equal to the parameter of the catenary, so that light rays coming from the focus of the catenary to points away from the apel; of the curve will he reflected converging'ly toward the axis of the curve.

Another wa)Y of deliuiiuga catenary in terms having; direct application to the problem of light reflection, isathat awcatenary is a curve in which the angle of refiection varies regularly and increasingly with relation to the axis of the curve as the angle of incidence is decreasedin 'lines drawn from the focus of the curve considering it as ay parabola but nevei` reaches an angle at right angles to the said axis.

A desired portion of the lower half of the refiector is formed as a parabola of rev' olution, said parahola having the same focus, as the catenary. In the diagram of Figure 2, I have shown part of the lower portion of the reflector as formed of such a parabola 4of revolution. The parabola is defined between lines 2-8, and is shown in Figure 1 Ain section at 3.

The remainder of the reflector, viz: the walls extending down from the central horizontal plane will be curved as regularly as possible so as to smoothly join with the two curved areas already noted. This portion of the reflector is indicated in Figura 2 as lying;` in the areas 4: and 5.

Now imagine a source of light located at the point 6 which is assumed to be the focus .of the catenary and of the parabola.

'The rays striking the parabola will be re flected in a straight line parallel to the axis of the parabola, which will form the narrow line of light lproviding features (a) above notcd. The rays of light striking the parabola are indicated by dotted lines 7.

The rays of light striking the catenary will be reflected almost vparallel with the axis thereof, at` the apex of theireflector, and asthey depart from the center will be gradually converged crossing the axis of the curve, at all times and gradually approaching in their pointof crossing of the axis, toward the focus of the curve.

Since all of the rays must cross the axis, which is a function of a catenary, it is evident that no rays caniescape upwardly, and shine in the eyes ofipassers-by since all rays will be reflected from a point above the plane of the axis, or exactly` on the plane thereof.

The rays of light from the portions 4; and 5 of the reflector will be thrown at a slant across the reflector and down, thereby brightly lighting the sides of the road close to the lampa.

The area of the portions 4 and 5, and the amount of the lower portion of the V refiector which will be defined by a parabola of revolution, will be determined from the light pattern required of the lamp. The horizontal component of the catenary portion of the retlector will be dcterrnined by the required light pattern also, (lependent upon the amount of light needed near the lamp, and the amount needed at the sides of the central beam at a distance from the .lamp

Referring to Figures 3 and 41', it will be noted that the reflector has a circular tlanve 8, having: the usual channel 9 for a fe lt strip, and that the space which is required to fill out the circle from the catenary is formed as part of the reflector, as at 10.

The catenary portion ,of the reflcctor is indicated at ll the parabolicportion atfl, and the two filling in curves at- 4; and 5, as in the` diagram.

Located in the reflector at the apex is a device formed of a metal ring 13, inia single plane, and set in the horizontal `plane of the lamp. This ring has a spherical section `ll, which is designedso as to act es an opaque body Cutting off `rays of llight which would elnanate from the bulb and miss striking 'the i'efiector at the front thereof, and above the said -horizontal planc. lt also has a sperical section 15, -which 'is designed to screen -that por-tion of the` apex of the reflector that would reflect rays toward the sphe-rical reflector in such a way as to ultimately result in light striking the parabolie portion thereof from other than its focus. Both of these Sections are formediwith a focus coincident with ;the focus of the parabolic portion of the l'efiector and at this focus the filament of the light bulb should be placed. There is a space between the two spherical Sections `suliicient to permit all light rays which can ``saifely be permitted to strike the upper portion of the reflector to iimpinge upon it directly. The concave faces of the i section ``are painted :white or silvered to act as refieotors, so that all light rays from the lamp are eventually emitted from ,the front `of the lamp body.

This device is described more fully in my pending application for patent Serial No. 662,111 filed September `11, 1923, to which reference is hereby made.

I include this device in .the present em' bodiment, in order to make it as perfect as possible, and it is evident that with the reflcctor built as I have now described it, and with the deflector unit installed, thelight rays all are conserved and none escape ;in other than a direction which can be mathematically predetermined.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

A lamp having a refiector formed with the part thereof above the horizontal `plane thereof as a catenary of revolution adapted to the parameter of the oatenary, and With to refleot rays of light strikng the same the intermediate portons from the horizonfrom a focus convergingly toward the horital plane to the beginning of the parabola 10 zontal axs of the reflector, and With a porcurved off to smoothly join the two curves 5 tion located centrally of the lower half of of revolution already noted.

the refleotor formed as a parabola of revolution having its focus at a distance equal JOHN H. LAIRD. 

